This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-115709, filed Apr. 13, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a MIS (Metal-Insulator-Semiconductor) field effect transistor and a method of manufacturing the same, particularly, to a MIS field effect transistor comprising a gate insulating film formed of a laminated insulating film comprising of a metal oxynitride film containing at least one metal selected from the group consisting of zirconium, hafnium and a lanthanoide series metal and an interface insulating film containing silicon and a method of manufacturing the same.
2. Description of the Related Art
A gate insulating film included in a CMOS (Complementary Metal-Oxide-Semiconductor) device in the sub-0.1 xcexcm era requires such a high specification as 1.5 nm equivalent oxide thickness. A SiO2 film having a thickness of 1.5 nm is poor in insulating properties and, thus, cannot be put to a practical use even in a logic device in which a high importance is placed on the high operating speed rather than on the increase in the power consumption caused by a leak current. Also, it is said indisputable that increasing demands are expected for an LSI device for a personal portable electronic equipment. The low power consumption is the greatest factor required for such an LSI device. Such being the situation, it is considered absolutely necessary to introduce a novel material that is markedly low in the leak current, compared with the conventional material of SiO2, for forming a gate insulating film the leak current density of which occupies a large portion of the power consumption of the entire device.
In order to realize an insulating film capacity of 1.5 nm equivalent oxide thickness and to obtain low leak characteristics, it is effective to utilize a material (high-K material) having a relative dielectric constant higher than that of SiO2 to increase the physical film thickness. For example, in the case of utilizing a material having a relative dielectric constant 10 times as much as that of SiO2, it is possible to set the physical film thickness required for obtaining a performance of 1.5 nm equivalent oxide thickness at 15 nm. As a result, it is possible to avoid the insulation breakdown of the film caused by the direct tunnel current. Incidentally, the high-K material noted above represents in general a metal oxide in which the high polarization based on its physical and chemical structure provides its high dielectric constant.
However, the metal oxide providing the high-K material has properties that are clearly inappropriate compared with SiO2 when the metal oxide is introduced into an LSI device as a gate insulating film. For example, the metal oxide in question is crystallized easily under relatively low temperatures, i.e., typically at 400 to 500xc2x0 C.
It should be noted that SiO2 or SiON used for forming a gate insulating film in the conventional LSI does not give rise to a change in the crystal state in any case to remain amorphous. The amorphous state prevents the impurity diffusion into silicon to improve the flatness of the insulating film and produces the effects that the leak current is lowered and that the nonuniformity in the characteristics among the elements of the LSI is suppressed. It follows that it is very important to use the insulating material capable of remaining amorphous for improving the yield of the LSI manufacture and the performance of the produced LSI device. Where the gate insulating film is crystalline, particularly, polycrystalline, it is expected that the particular effects pointed out above, which were naturally obtained in the past, may be lost to lower the yield and, in addition, to make it difficult to obtain the desired performance. Under the circumstances, required is a gate insulating film material, which has a dielectric constant higher than that of SiO2 and which is not easily crystallized under high temperatures employed in the LSI process.
A mixed oxide including silicon oxide and an oxide of a metal other than silicon is being studied as one of the materials satisfying the requirements pointed out above. The typical examples of the particular mixed oxide include, for example, Tixe2x80x94Sixe2x80x94O, Zrxe2x80x94Sixe2x80x94O, Hfxe2x80x94Sixe2x80x94O and Laxe2x80x94Sixe2x80x94O. These materials are capable of remaining amorphous even under such a high temperature as 1,000xc2x0 C., or capable of retaining an amorphous state required for a matrix of an insulating film, though crystallization takes place partially in these mixed oxides.
However, such a mixed oxide gives rise to the problem that, if silicon is added to the mixed oxide for improving the amorphous state, the relative dielectric constant of the mixed oxide is markedly lowered. In view of the fact that the relative dielectric constant of the mixed oxide (or an alloy oxide) is determined by the average dielectric constant of the metal oxide and SiO2, the relative dielectric constant falls within a range of between 10 and 15 in the case where the alloy is prepared on the basis of the component ratio of, for example, 1:1. Further, where a metal oxide is added to SiO2 at a high ratio of 1:1, the mixed material fails to maintain the amorphous state in general. In practice, it is impossible for the mixed material to maintain the amorphous state unless the mixing ratio of silicon oxide to the metal oxide is about 3:1. The relative dielectric constant of the mixed material in this case is lowered to 10 or less without fail. In view of the fact that the effective relative dielectric constant of, for example, SiON used for forming a gate insulating film of a device actually used nowadays is about 6, the relative dielectric constant of the silicon-metal oxide mixed material that is studied nowadays produces the effect of increasing the physical film thickness to a level only about 1.5 times as much as that of SiON. Even if the leak current can be relatively lowered by the use of the particular mixed material, it is expected that the mixed material will be a material of a short life that can be utilized in a device of only one era.
As described above, for improving the amorphous state, an alloy oxide containing silicon and another metal is used mainly for providing a material of the high-K gate insulating film replacing the conventional SiO2 material and SiON material. However, the relative dielectric constant of the alloy oxide noted above is only about 10 and, thus, the alloy oxide fails to provide a material of a gate insulating film that can be used over a plurality of eras.
An object of the present invention is to provide a MIS field effect transistor comprising a gate insulating film containing a high-K material and having a relative dielectric constant substantially equal to that of a metal oxide.
Another object of the present invention is to provide a method for manufacturing a MIS field effect transistor comprising a gate insulating film capable of markedly suppressing the crystallization of the high-K material during the heat treatment to improve the resistance to heat and having a relative dielectric constant substantially equal to that of the metal oxide.
According to one aspect of the present invention, there is provided a MIS field effect transistor, comprising:
a silicon substrate;
an insulating film formed over the silicon substrate and containing silicon and at least one of nitrogen and oxygen;
a metal oxynitride film formed on the insulating film and containing at least one kind of metal atom selected from the group consisting of zirconium, hafnium and a lanthanide series metal, the metal oxynitride film containing nitrogen atom not bonding with the metal atom without metal-nitrogen bond at the density of higher than 1019/cm3; and
a gate electrode formed on the metal oxynitride film.
According to another aspect of the present invention, there is provided a MIS field effect transistor, comprising:
a silicon substrate;
an insulating film formed over the silicon substrate and containing silicon and at least one of nitrogen and oxygen;
a metal oxynitride film formed on the insulating film and containing at least one kind of metal atom selected from the group consisting of zirconium, hafnium and a lanthanide series metal, the nitrogen atom being substantially bonded to nitrogen or oxygen; and
a gate electrode formed on the metal oxynitride film.
Further, according to still another aspect of the present invention, there is provided a method for manufacturing a MIS field effect transistor, comprising:
supplying at least one metal selected from the group consisting of zirconium, hafnium and a lanthanide series metal over a surface of a silicon substrate together with nitrogen to form a metal nitride film;
annealing the surface of the silicon substrate and the metal nitride film to convert the metal nitride film into metal oxynitride film and to form an insulating film containing at least one of nitrogen and oxygen and silicon between the surface of the silicon substrate and the metal oxynitride film, thus obtaining a gate insulating film; and
forming a gate electrode on the gate insulating film.